Ball Grid Array (“BGA”) techniques are commonly used for producing high-density integrated circuit (“IC”) components. A regular array of solder balls is deposited onto the IC component at contact pads where the electrical contacts of the IC component are to be formed. Such balls forming the electrical contacts of the IC component may then be mated with corresponding connections on a printed circuit board in use.
During production using BGA techniques, droplets of flux and solder balls must be transferred to a substrate where they are deposited in a predetermined array. A common technique is to use a flux transfer head or pin head to transfer flux to the substrate and a ball pick head to carry solder balls in the same array configuration as is required on the substrate, and then subsequently to deposit balls onto the substrate containing flux. It is usually essential that all the electrical contact points of the IC component are covered by solder balls to ensure that the component is not defective. Conventionally, the ball pick head is formed with a plurality of locations for receiving solder balls, these locations being disposed in the same array configuration as the desired configuration of solder balls on the circuit board. The corresponding pin head must also deposit flux droplets in the same array configuration on the substrate.
A number of challenges are presented to the design of fast and efficient apparatus for the placement of flux droplets and solder balls. The apparatus must be designed so that the pin head and the ball pick head are brought in turn to a precise position over the substrate and since the dimensions of the array and in particular the spacing between solder ball locations on the array are small, accurate alignment techniques must be employed. Generally, a vision or pattern recognition system such as a camera is used to locate and capture images of at least two fiducial markers on the substrate to determine whether any degree of movement is required to achieve alignment with the substrate.
The need in a production process to accurately align pin heads and ball pick heads over the substrate in a high-speed and efficient manner has given rise to the use of two cameras to reduce the movement that might be required by a single camera having to travel between the fiducial markers. An example is U.S. Pat. No. 6,070,783 in respect of a “Conductive Ball Attaching Apparatus and Method”. An apparatus is described wherein two alignment cameras are diagonally positioned from each other and integrated to a main transfer means. The problem is that the main transfer means is involved in many process work elements, such as ball pick-up, flux transfer, alignment and ball placement on the substrate. Moreover, the apparatus has a large transfer means design, such that the individual transfer means need to travel a relatively long distance to complete one cycle, resulting in a longer alignment and ball placement process. Another feature of the apparatus is that the cameras are rigidly integrated with the transfer means, such that movement of the cameras is dependent on movement of the transfer means. This makes the system more cumbersome and complex.
Another example of an apparatus using two cameras to align a substrate is U.S. Pat. No. 6,355,298 for a “Placement System Apparatus and Method”. One alignment camera is mounted on a pin head and another camera is mounted on a ball pick head. The ball pick head is involved in a time-critical process and has a higher number of process work elements as compared with the pin head. The result is an unequal distribution of work-loading since the ball pick head takes a significantly longer time to complete its processes as compared to the pin head. The ball pick head is not able to perform simultaneously a ball pick-up process (which includes ball preparation into a predetermined array for pick-up) and substrate alignment. This is because the ball pick head needs to wait for the processed substrate to exit the ball mounting station and a new substrate to enter for alignment, before it can perform ball preparation for another substrate. The waiting time contributes to increased process cycle time.